- Oak Ten
- Oaken Shield
- Oblivion
- Ocean Music
- Ocean Rain
- Octopus Electrical
- Odeon
- Odeon Fonográfica
- Odette Prod
- Odissey
- Off Beat
- Off Course, EMI Electrola
- Off The Hip
- Oglio
- Oh'Zone
- Ohio Gold
- Ohlone
- Ohr
- OIHUKA
- Old
- Olsen
- Olympic
- Ombrage Editions
- On The Camper
- On-U Sound
- One Flash
- One Foot
- One Hour/Jagjaguwar
- One Little Indian
- One Louder
- One Way
- One-handed Music
- Onion Productions
- Only Lovers Records
- Onlyforever Recordings
- Onomania
- Opax
- Opposite Prod
- Optical Sound
- Orange Twin
- Orchard
- Organik
- Orkhestra
- Osmose
- Osmose Productions
- Other Tongues
- Ottonecker
- Ouga Booga And The Mighty Oug
- Oui Oui
- Our!
- Out Of The Blue
- Out Post
- Outer Battery
- Outpost
- Output
- Overcoat
- Overcome
- Overdraft
- Overground
- Own